Ideally a human eye lens receives light from an object and bends it in such a way that an image of the object is resolved upon the photoreceptor cells at a small area of the retina called the macula. The retina is the nerve fiber layer in the interior of the eye, with the macula being the most sensitive area of the retina receiving visual images. In order to maintain focus on the macula, the eye's lens must change its shape when objects are viewed from near distances. The human cornea also serves to focus incoming light. The cornea has more focusing power than the lens. In any case, if the cornea-lens combination focuses light rays from a viewed object at a point in front of the retina, the person is thereby rendered myopic, also commonly called nearsighted. In effect, the image projected onto the photoreceptor cells of the macula on the retina appears blurred and out of focus. Myopia often occurs when the eyeball grows too long for the normal focus of the cornea and the lens. An eye of normal size also can develop myopia if the curvature of the cornea and/or lens increases, thereby producing greater refractive power (bending of light).
A myopic person's distance vision is blurred, but that person has good near vision until reaching the age of between 40-45 years, when presbyopia becomes a factor due to the hardening of the lens inside the eye. This condition can usually be corrected by the use of glasses or contact lenses having a convex front surface and a concave back surface with a smaller radius.
Conversely, if light rays from a viewed object are focused at a point behind the retina, the person is thereby rendered hyperopic or farsighted. This defect in the refraction of light coming into the eye diminishes the person's ability to see objects at varied distances. In hyperopic patients, rays of light coming from distant objects are not properly focused on the retina and those coming from nearer objects (say, within 20 feet) also are out of focus. The physical causes of farsightedness may be (1) too short an eyeball, (2) insufficient convexity of the eye's lens and/or (3) changes in the refractive media of the eye. In most cases farsightedness is correctable by the use of glasses or contact lenses having suitable convex lens systems.
Next it should be noted that the pupil of the eye acts as the limiting aperture through which all light from an object being viewed must pass. Thus, for any given pupil size, the size of the pupil aperture will determine the relative contribution of light from near objects.
In addition to the eye conditions of hyperopia and myopia, when a person reaches 40-45 years of age he or she also becomes presbyopic, i.e., unable to focus clearly on objects at near ranges regardless of whether the patient is hyperopic or myopic or ametropic (without a defect). This condition can be corrected by bifocals or reading glasses or multi-focal (bifocal) contact lenses.
The term "astigmatism" is applied to a condition wherein light rays emanating from a viewed object are not focused as a single point by the eye's optical system, but rather are focused (usually at right angles to each other) as two line images at different distances along an optical axis of the eye. Astigmatism usually has its genesis in irregularities in the shape of the cornea. For example, a cornea may not be truly spherical; it may be slightly flattened or contain a bulge, either horizontally or vertically. Astigmatism is manifested by a variety of vision distortions. For example, in looking at an object, a straight line in the vicinity of that object may appear curved to a person suffering from some forms of astigmatism. Another manifestation might be that, when the eyes are moved, a motionless object may seem to move as it passes through the field of vision of an astigmatically distorted area of an eye. Astigmatism can be horizontal, vertical, or diagonal.
In general, artificial correction of the above-noted vision problems by use of contact lenses follows from the fact that precise changes in their refracting power can be created through the use of differences in the radii of curvature of the opposing surfaces of such a lens. For example, when the radius of curvature of the outer surface of a contact lens is greater than the surface next to the eye, or the back surface, the lens provides plus refractive power. Conversely, when the radius of curvature of the outer surface of the optical portion is less than the radius of curvature of the inner surface, minus refracting power is obtained. "Plano" power is obtained when the two radii are equal. Hence, aside from changes in the chemical compounds from which contact lenses, and especially soft contact lenses, are made, most innovative steps concerning contact lenses involve changes in the geometry of the elements of such lenses in order to: (1) improve vision, (2) maintain the angular orientation of the lens with respect to the eye and/or (3) move the lens up or down through action of the eyelid.
It also should be noted that, because the role played by the brain in processing light--carried information (i.e., reducing it to "vision") is not completely understood, the efficacy of such changes in vision are based upon experience as well as upon application of the principles of optics. That is to say that, "seeing" and "vision" are highly complex phenomena that involve the eye (as the organ of seeing) as well as the brain (the organ of vision). And, as with any function involving the brain, these phenomena are subject to the influences of many variables. For example, since near and distant focal planes are focused on the retina simultaneously, the observer's brain must, in effect, "select" the desired image and suppress the unwanted image. Such suppression and selection of images has been well documented, but it is not well understood. Some psychometric studies have strongly suggested that a person will see an object in spite of visual "noise" (light that does not contribute to the image of the object of regard) by virtue of the brain's ability to "ignore" the unselected images. Such studies also have suggested that the direction of a person's gaze and the location of the desired object also are factors in the brain's processing of light-carried information. It also has been established that "unselected" images, and especially those that lie peripheral to the line of sight, are somehow less effective in stimulating the brain's photoreceptor cells. The ability of artificial lenses to influence the brain's processing of photoreceptor-induced electrical stimuli of near and distant images also has been well established, but not fully understood. Indeed, the multifocal soft, contact lenses of this patent disclosure, in ways that are not completely understood, make use of the brain's own ability to process light-carried information in desired ways.
Some elaboration of this important effect is in order. Conventional bifocal spectacles, and rigid bifocal contact lenses, have called for the user to somehow position the near vision lenses to view the near object of regard. A different segment of the lens would be used to see more distant objects; this might be accomplished by the user's moving the lenses slightly with an eyelid, or the spectacle wearer's tilting his head downward to view through the upper portion of his glasses. This effect is known as "translation." By contrast, applicant's design calls for the user to look through the near vision and far vision portions of the lens simultaneously at all times. Near and far vision are both constantly available for selection or rejection by the user's brain, with no adjustment of the lenses or eyes or head to the object being viewed.
The lens design features used by applicant to achieve these results are, to some degree, loosely scattered throughout the patent literature. For example, U.S. Pat. No. 4,126,138 teaches a soft contact lens having a carrier portion and a central optical portion wherein the radius of curvature of the outer surface of the optical portion is described as being greater than, or less than, the curvature of the eye contacting inner surface. Thus, the lens can provide either far vision correction or near vision correction. Variation in the refractory power of this lens is described in terms of the height of an optical portion of the outer surface of the lens above the height of its carrier portion-relative to the height of the optical portion. A sloping interconnect portion of this lens system is generally described as "either a flat or slightly outwardly or inwardly curved surface". The slope of the interconnect portion also is described as being determined by the values of certain dimensions of various elements of the lens.
U.S. Pat. No. 4,752,123 discloses a bifocal contact lens with three distinct concentric zones. The first is a centrally positioned, far-vision correction zone of circular periphery. Preferably this zone has a diameter of from about 0.5 to 1.5 mm. This far-vision correction zone is surrounded by a near vision correction zone having a diameter of about 2.35 mm. A third, outer vision-aiding zone, having an outer diameter of 7.00 mm, surrounds the near vision correction zone.
U.S. Pat. No. 4,869,587 teaches a contact lens having two concentric annular areas. In one embodiment of this lens, an annular central area provides near vision correction. An outer annulus surrounds the central area and is configured to provide distant vision correction. Moreover, these two zones can be arranged to accommodate an intermediate annular area for making intermediate corrections. This patent also discloses use of a small peripheral curve for fitting the lens to the eye.
U.S. Pat. No. 4,636,049 discloses a contact lens having two distinct vision correction regions. They are formed by use of two different curves on the front surface of the lens. A first, centered, zone is characterized as "a near power correction region". It is surrounded by a concentric, distance correction zone. The near power correction zone also is described as having a rear surface area equal to about one half of the pupil area of a normal eye under normal reading light conditions.
U.S. Pat. No. 5,141,301 discloses a soft toric contact lens having a distance-vision correction portion and a near-vision correction portion. The near-vision portion is located in the upper and side regions of the optical zone. The circular design is of equal reading segment size all around the distance-vision correction portion. The lens also is thicker near its upper edge. Hence, as the upper eyelid moves down, it pushes the lens downward.
U.S. Pat. No. 4,084,890 discloses a soft contact lens having a centrally located optical zone surrounded by a peripheral portion that extends outwardly from the optical zone to a relatively thin outer edge zone. The outer edge zone is thicker than either the edge or the juncture of the optical zone. It also is thicker than the peripheral portion.
U.S. Pat. No. 5,071,244 teaches a soft contact lens system having a central portion formed to the distance correction prescription of the user and a small auxiliary lens formed to the close up prescription of the user. The auxiliary lens is located on the lower margin of the lens.
French Patent 2,688,898 discloses a lens whose anterior surface has a thicker add portion having a diameter of 1 to 3 mm and a thickness between 2.times.10.sup.-3 and 0.05 mm. The sides of the add portion are characterized as being in the shape of a "truncated cone". No precise description of the angle of decline of this truncated cone is given.
All of these innovations notwithstanding, there still is room for making improvements in soft contact lens. This is true both with respect to the ability of such a lens to correct for presbyopia as well as maintaining its proper position on the cornea for long periods of time. There is even more room for improvement in giving soft, bifocal contact lenses that are used for correcting presbyopia, the added capability of correcting for astigmatism and maintaining the lens in the proper angular orientation with respect to the astigmatism. The soft, bifocal, contact lenses of this patent disclosure provide such improvements.